Oh, you want to know how Japan became this peaceful. Easy:
First, after decades of isolationism, they decided to conquer everything around them up until the second World War, when they decided to ally themselves with the wrong side of History and picked a fight with a Juggernaut.
After countless air raids, 2 atomic bombs and Japanese concentration-- hum, I mean "internment" camp, they decided to surrender to said Juggernaut. With its help, they revolutionized their industry, became an incredibly rich country in a very short time which is why they can now live as a prosper and peaceful nation.